How to limit a group of users and let them be ONLY able to send to and receive from another group of users?

http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/7a12dd3a-ab9e-41a5-af42-6087be993559/

Hi,
We can configure transport rule to restrict send messages.
Apply rule to messages
from a member of team1@xxx.com
Delete the message without notifying anyone
except when the message is sent to member of team2@xxx.com /except when any of the recipients in the To field is a member ofteam2@xxx.com.
We can use Message Delivery Restriction settings to restrict to receive messages.
1. Right click on team1@xxx.com and properties.
2. Navigate to "Message Delivery Restriction".
3. Select only senders in the following list.
4. Add team2@xxx.com to the list.
Regards,
Xiu